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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.reference.async_read_until.overload2"></a><a class="link" href="overload2.html" title="async_read_until (2 of 8 overloads)">async_read_until
        (2 of 8 overloads)</a>
</h4></div></div></div>
<p>
          Start an asynchronous operation to read data into a dynamic buffer sequence
          until it contains a specified delimiter.
        </p>
<pre class="programlisting">template&lt;
    typename <a class="link" href="../AsyncReadStream.html" title="Buffer-oriented asynchronous read stream requirements">AsyncReadStream</a>,
    typename <a class="link" href="../DynamicBuffer.html" title="Dynamic buffer requirements">DynamicBuffer</a>,
    typename <a class="link" href="../ReadHandler.html" title="Read handler requirements">ReadHandler</a>&gt;
<a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_read_until(
    AsyncReadStream &amp; s,
    DynamicBuffer &amp;&amp; buffers,
    string_view delim,
    ReadHandler &amp;&amp; handler);
</pre>
<p>
          This function is used to asynchronously read data into the specified dynamic
          buffer sequence until the dynamic buffer sequence's get area contains the
          specified delimiter. The function call always returns immediately. The
          asynchronous operation will continue until one of the following conditions
          is true:
        </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
              The get area of the dynamic buffer sequence contains the specified
              delimiter.
            </li>
<li class="listitem">
              An error occurred.
            </li>
</ul></div>
<p>
          This operation is implemented in terms of zero or more calls to the stream's
          async_read_some function, and is known as a <span class="emphasis"><em>composed operation</em></span>.
          If the dynamic buffer sequence's get area already contains the delimiter,
          this asynchronous operation completes immediately. The program must ensure
          that the stream performs no other read operations (such as async_read,
          async_read_until, the stream's async_read_some function, or any other composed
          operations that perform reads) until this operation completes.
        </p>
<h6>
<a name="asio.reference.async_read_until.overload2.h0"></a>
          <span><a name="asio.reference.async_read_until.overload2.parameters"></a></span><a class="link" href="overload2.html#asio.reference.async_read_until.overload2.parameters">Parameters</a>
        </h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">s</span></dt>
<dd><p>
                The stream from which the data is to be read. The type must support
                the AsyncReadStream concept.
              </p></dd>
<dt><span class="term">buffers</span></dt>
<dd><p>
                The dynamic buffer sequence into which the data will be read. Although
                the buffers object may be copied as necessary, ownership of the underlying
                memory blocks is retained by the caller, which must guarantee that
                they remain valid until the handler is called.
              </p></dd>
<dt><span class="term">delim</span></dt>
<dd><p>
                The delimiter string.
              </p></dd>
<dt><span class="term">handler</span></dt>
<dd>
<p>
                The handler to be called when the read operation completes. Copies
                will be made of the handler as required. The function signature of
                the handler must be:
</p>
<pre class="programlisting">void handler(
  // Result of operation.
  const asio::error_code&amp; error,

  // The number of bytes in the dynamic buffer sequence's
  // get area up to and including the delimiter.
  // 0 if an error occurred.
  std::size_t bytes_transferred
);
</pre>
<p>
                Regardless of whether the asynchronous operation completes immediately
                or not, the handler will not be invoked from within this function.
                Invocation of the handler will be performed in a manner equivalent
                to using <code class="computeroutput">asio::io_context::post()</code>.
              </p>
</dd>
</dl>
</div>
<h6>
<a name="asio.reference.async_read_until.overload2.h1"></a>
          <span><a name="asio.reference.async_read_until.overload2.remarks"></a></span><a class="link" href="overload2.html#asio.reference.async_read_until.overload2.remarks">Remarks</a>
        </h6>
<p>
          After a successful async_read_until operation, the dynamic buffer sequence
          may contain additional data beyond the delimiter. An application will typically
          leave that data in the dynamic buffer sequence for a subsequent async_read_until
          operation to examine.
        </p>
<h6>
<a name="asio.reference.async_read_until.overload2.h2"></a>
          <span><a name="asio.reference.async_read_until.overload2.example"></a></span><a class="link" href="overload2.html#asio.reference.async_read_until.overload2.example">Example</a>
        </h6>
<p>
          To asynchronously read data into a <code class="computeroutput">std::string</code> until a CR-LF
          sequence is encountered:
        </p>
<pre class="programlisting">std::string data;
...
void handler(const asio::error_code&amp; e, std::size_t size)
{
  if (!e)
  {
    std::string line = data.substr(0, n);
    data.erase(0, n);
    ...
  }
}
...
asio::async_read_until(s, data, "\r\n", handler);
</pre>
<p>
          After the <code class="computeroutput">async_read_until</code> operation completes successfully,
          the string <code class="computeroutput">data</code> contains the delimiter:
        </p>
<pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n', 'd', 'e', ... }
</pre>
<p>
          The call to <code class="computeroutput">substr</code> then extracts the data up to and including
          the delimiter, so that the string <code class="computeroutput">line</code> contains:
        </p>
<pre class="programlisting">{ 'a', 'b', ..., 'c', '\r', '\n' }
</pre>
<p>
          After the call to <code class="computeroutput">erase</code>, the remaining data is left in the
          string <code class="computeroutput">data</code> as follows:
        </p>
<pre class="programlisting">{ 'd', 'e', ... }
</pre>
<p>
          This data may be the start of a new line, to be extracted by a subsequent
          <code class="computeroutput">async_read_until</code> operation.
        </p>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2018 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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